The Greek government has announced plans to hold illegal immigrants in indefinite detention if they are considered a risk to public health, drawing sharp criticism from the human rights group Amnesty International, which called the proposals "deeply alarming".

In draft legislation submitted to parliament, the government requested the backing of politicians to hold immigrants in detention for compulsory health checks and treatment for HIV/Aids and other contagious ailments.

Greece, which is due to hold a general election either in late April or early May, is the European Union's busiest transit point for illegal immigrants.

Last week the government launched police roundups of illegal immigrants in Athens, with hundreds of people being subjected daily to street stops by police.

"Under the proposed amendments, the law will foresee the right to detain non-nationals – whether they have applied for political asylum or not – if they pose a risk to public health," the authors of the bill submitted late on Monday wrote.

Immigrants liable for detention, it said, posed a risk "because they have contracted an infectious disease, or because they belong to groups vulnerable to such diseases, like intravenous drug users, persons involved in [prostitution] or people who reside in conditions that do not meet the elementary standards of hygiene".

The document was signed by the Greek ministers of finance, health and public order. It said: "The subjects … will be submitted to compulsory health examinations and corresponding treatments.

"Treatment areas will be subject to detention regulations for the period that the reasons for their detention apply."

The law is due to be put to the vote in parliament before 11 April.

The government argues it has little choice other than to take tougher measures, estimating that more than a million illegal immigrants live in Greece, which has an official population of 11 million.

Amnesty urged Greece not to go ahead with the new proposals.

"These deeply alarming measures specifically target the most vulnerable people based on discriminatory criteria," said Amnesty's Jezerca Tigani.

"The Greek authorities must withdraw such measures immediately, which will only exacerbate the stigmatisation of migrants and asylum-seekers in the country."